Overview Our Small Angle Scattering Core provides state of the art instrumentation and expertise for the acquisition and interpretation of X-ray and neutron scattering data from proteins, protein complexes and assemblies in solution, as well as necessary associated facilities for protein production and biochemical and biophysical characterization. We have "in house" capabilities for X-ray solution scattering (at the University of Utah and University of Sydney), and we will use neutron scattering facilities at the OPAL Research Reactor at Australian Nuclear Science and Technology Organization (ANSTO). Each protein or protein assembly to be studied will require extensive characterization first with X-ray scattering to establish that the systems meet the stringent requirements for solution scattering: monodisperse identical particles and the ability to either approximate dilute solution conditions or to acquire data over a range of concentrations and extrapolate to the infinite dilution condition. This work will primarily be performed at the University of Utah to facilitate the close interactions required with the HIV protein biochemistry expertise. Once these conditions are established and we have learned all that we can from the X-ray experiments, neutron contrast variation experiments on the complexes targeted for study can be planned and implemented using the resources available at the University of Sydney. The neutron contrast variation studies will require the preparation of relatively large amounts (10-20 mg) of highly purified, deuterated protein components. This work will be done at the University of Sydney where we have extensive, modern laboratory facilities for fermentation, protein expression and purification, and biochemical and biophysical characterization. We also have access to inexpensive sources of heavy water (enrichments in the range 97-99.95% 2H) through Dr Trewhella's association with the Bragg Institutes at ANSTO. The existing X-ray scattering facilities at Sydney will be used to evaluate any potential effects of deuteration on the solution behavior of the systems to be studied. The neutron scattering studies will be done using QUOKKA at the OPAL Research Reactor at ANSTO. This new reactor facility was completed in 2006 (currently running at full power, 20 MW) and the new small-angle neutron scattering instrument (QUOKKA) is scheduled to be complete by July 2007. As part of her Federation Fellowship offer, Dr Trewhella was granted 30 days per year of beam time on QUOKKA, and she is dedicating up to 10 days/year of this time to this project - sufficient time for 4 complete neutron contrast variation experiments. Should there be any delay in the schedule for QUOKKA coming on line for experiments, the aims for the Center will not be delayed as we will apply for the needed neutron beam time at NIST on NG-3, an instrument that Dr Trewhella is regularly successful in obtaining beam time through the normal proposal submission processes there (10 days in 2006, 8 days allocated for 2007). QUOKKA will be the preferred instrument for measurement as we have had the opportunity for input into its design and thus this instrument will have the sample configuration that optimizes for small-sample volumes and thus greatly reduces the demands on deuterated sample production. Dr Trewhella has established effective means for transporting materials between Sydney and the US, using commercial carriers (FedEx, UPS) and in the case of importing plasmids, organisms, and protein materials the School of Molecular and Microbial Biosciences at USyd already has an AQIS permit in place to facilitate fast progress through Australian customs and quarantine. In the case that some of the early neutron scattering experiments are to be done at NIST, samples will be hand carried by the experimenters as has been done by Dr Trewhella for experiments in 2006 she completed at NIST.